Patent GB-1482104-A (GB)
Title: Localizer or glide-slope facility
IPC: G01S1/14
Filed: 1974-10-29
Abstract: 1482104 Radio navigation INTERNATIONAL STANDARD ELECTRIC CORP 29 Oct 1974 46796/74 Heading H4D In an I.L.S. localizer or glide-slope arrangement two transmitters S1 S2, Fig. 1 are provided, each having two outputs, i.e. one output comprising signals of carrier and of sideband frequencies, and the other output comprising signals of sideband frequencies only. The carrier frequencies of the two transmitters differ, e.g. by 9 kHz, and a control unit 16 is provided whereby, during normal operation, the outputs of the transmitters are coupled to an associated aerial system such that a two-carrier system is provided. In this, the outputs of one transmitter provide a clearance radiation pattern and those of the other provide a course radiation pattern, the capture effect of an aircraft receiver being made use of as the aircraft approaches the correct course. However, should one transmitter fail, the control unit switches the outputs of the other transmitter in such a way that operation continues as a one-carrier system. As described, the transmitters S1, S2 comprise respective 90 Hz modulators 3, 5 and 150 Hz modulators 4, 6 which receive power at carrier frequencies from oscillators 1, 2, and which are coupled to respective input ports of bridges 7, 8. The "sum" outputs of said bridges are applied to switches X, and the "difference" outputs thereof to switches Y. For normal operation, as shown in Fig. 1, the "sum" output from the bridge 7 is applied through the switch X and through a switch B and a switch A to an input E1 of a power distributer 9, which feeds the aerial system. In a similar way, the "sum" output from the bridge 8 is applied through switches X and C to an input E2. The "difference" output from the bridge 7 is applied through switches Y, F and E to an input E4. In a similar way, the "difference" output from the bridge 8 is applied through switches Y and D to an input E3. A monitoring facility is provided which, if a transmitter fails, automatically sends a signal to the control unit 16, whereupon the localizer or glide-slope arrangement is switched to one-carrier operation by control signals K1 or K1+K2. If the transmitter S2 fails, the control signal K1 alone is given, and it causes the switches A, B, C, D, E, F to change over (as shown by broken lines) whilst the switches X, Y remain as they were. The "sum" output from the bridge 7 is applied to the input port a1 of a bridge 10, and the "difference" output from the bridge 7 is applied to the input port a2 of a bridge 11. Respective outputs from ports d1, d2 of the bridges 10, 11 are applied directly to the inputs E1, E4 of the power distributer 9, while respective outputs from ports b1, b2 of the bridges 10, 11 are applied via attenuators 12, 14 and phase shifters 13, 15 to the inputs E2, E3. The said attenuators and phase shifters are used to adjust the amplitudes and phases of the power inputs at E2, E3 in relation to those at E1, E4. The output ports of the inoperative transmitter S2 are coupled to terminating impedances f1, f2. If the transmitter S1 fails, both control signals, K1 and K2, are given and the switches X and Y changeover, as well as the switches A, B, C, D, E, F.